1. Field of the Invention
This invention relates to barrier layers.
2. Background of the Invention
The introduction of CVD metal diffusion barriers into mainstream Back End of Line semiconductor manufacture is becoming increasingly more common. Due to the continued shrinking of device feature sizes traditional PVD techniques such as long throw and collimated sputtering have been superseded by ionised sputtering techniques that offer impressive increases in bottom coverage. However, for Cu metallisation a very thin but effective barrier material is needed in contact with the interlayer dielectric (ILD) to prevent Cu diffusion and so the conformality of deposition is paramount. Atomic layer CVD (ALCVD) offers seemingly perfect conformality and high purity layers with good diffusion barrier properties. Use of ALCVD technology as a diffusion barrier is however not without its problems; high resistivity materials, low deposition rates and ALCVD's sensitivity to surface conditions are some of the issues currently under investigation. Metal organic CVD (MOCVD) is seen as a promising technology due to its higher deposition rate, good conformality and relatively low process temperatures but has the difficulty in meeting the challenge of producing a robust low resistivity barrier to Cu diffusion.
Significant efforts have been made to develop metal organic (MO) precursors for the MOCVD of both TiN and TaN, materials with good adhesion to ILDs and excellent diffusion barrier characteristics to Cu. Thin films deposited from such precursors systems however have been found to have high resistivity, mainly due to the incorporation of large amounts of C and H within the growing film. Poor conformality due to significant gas phase reaction can also be a drawback.
So-called “amorphous TiN” has been reported in the literature, but, as discussed in more detail below, all known examples contain crystallites. For many uses of bulk materials, the presence of these crystallites may be irrelevant. However, as indicated above, barrier layers for ILD are extremely thin and are approximately the same thickness as the dimensions of the crystallites. The presence of such crystallites would therefore prevent such materials forming effective barrier layers and these materials have therefore been discounted for this use.